It looks like bug 8165 https://bugs.maemo.org/show_bug.cgi?id=8165

Try to kill gst-video-thumbnailerd via X-Term command:

killall gst-video-thumbnailerd

If helps - please vote for that bug.

Note: sometime it has sense to kill mafw-gst-renderer - do "ps|grep mafw-gst-renderer" and "kill XXX" where XXX is a process id from previous command. I found that after playing some videos the regular video renderer grows big in memory and that may be a problem. If that helps - feel free to vote for bug 7147 https://bugs.maemo.org/show_bug.cgi?id=7147